In optoelectronic modules used in the various communications fields, one of the most difficult problems that must be solved is the efficient transmission of light between a light generating device and an optical fiber or, alternatively, the transmission of light from the optical fiber to a light receiving device. Here it will be understood by those skilled in the art that the term “light” is a generic term which includes any electromagnetic radiation that can be modulated and transmitted by optical fibers or other optical transmission lines. Because optical fibers and the active regions of light generating devices and light receiving devices are very small, alignment of an optical fiber with a light generating device or a light receiving device is difficult and can be very work intensive and time consuming.
For example, one method used to align an optical fiber with a light generating device or a light receiving device is called active alignment. In this process a light is introduced at one end of the optical fiber and the other end is moved adjacent the active area of an operative light receiving device, while monitoring the output of the light receiving device, until a maximum output signal is received. Alternatively, an operative light receiving device is attached to one end of an optical fiber and the other end is moved adjacent the active area of an operative light generating device until a maximum output signal is received. In both instances the amount of time and effort required to obtain the optimum alignment is extensive.
In some systems, generated light passes directly into an optical fiber and exits the optical fiber where the light is directed onto an active surface of a light receiving device. However, in the real world much of the generated light travels outwardly in a direction to miss the optical fiber and some of the light impinging on the optical fiber is reflected back into the light generating device. Much of the cause of this outwardly or misdirected light comes from poor alignment along the Z axis (the axis of light propagation) as well as misalignment in the X and Y axes (defining a plane perpendicular to the direction of light propagation). The outwardly or misdirected light can impinge on adjacent devices to produce unwanted cross-talk within the system.
The reflected light can be directed back into the light generating device or the optical fiber can interfere with generated light to produce unwanted and troublesome modes or frequencies. Also, the loss of light through misdirection and/or reflection means that additional power must be used to produce sufficient light to transmit between various devices, thus increasing power dissipation.
The vast majority of optoelectric device-to-optical fiber use either one lens (a focusing lens) or two lenses (one lens to collimate and one lens to focus). Each of these approaches have pros and cons when it comes to optical alignment tolerances. The one-lens design has tight lateral (x and y directions) tolerances but loose tilt tolerances. The two-lens design is the opposite, i.e. loose lateral tolerances but tight tilt tolerances. Therefore, neither of these designs overcomes the alignment and, thus, the assembly problems that cause a large amount of the failures and the cost of the product.
Also, in optoelectronic modules it is usual to require that the return loss measured into the transmitter optical subassembly (TOSA) be 27 dB minimum. Conventionally, to reduce light reflection back into the laser or other optoelectric device, the adjacent facet of the optical fiber is angled relative to the optical axis (Z-axis). The angled facet forces the focusing optics to be tilted relative to the core of the optical fiber. This tilting adds further complications to the original design and the assembly of the optoelectronic module.
It would be highly advantageous, therefore, to remedy the foregoing and other deficiencies inherent in the prior art.
Accordingly, it is an object the present invention to provide a new and improved optoelectric subassembly for an optoelectronic module.
Another object of the present invention is to provide a new and improved optoelectric subassembly with lower lateral and tilt tolerances that can be easily manufactured and assembled.
Another object of the present invention is to provide a new and improved optoelectric subassembly with high optical return loss (i.e. low reflection into the optoelectric device).
Another object of the present invention is to provide a new and improved optoelectric subassembly for an optoelectronic module which greatly increases the life and reliability of the mechanism and the optoelectronic module.